We are requesting funds for the purchase of a fluorescence lifetime instrument. Our particular requirements necessitate the ability to measure lifetimes as short as 0.4 ns, to be able to measure the decay of fluorescence anisotropy, and the ability to analyze decay curves for heterogeneity of fluorescence decay. Our major users group consists of a group of four scientists who share a common interest in the relationship between membrane structure and function. Use of this instrument in five specific projects is discussed: Dr. David Wolf, Fluorescence Studies of the Segregation of Membrane Lipids and Proteins; and Change in Membrane Structure During Sperm Capacitation; Dr. Grant Fairbanks, Fluorescent Probe Studies of Structure Transitions in Normal and Abnormal Red Blood Cell Membranes; Dr. Steven Treistman, Fluorescent Probe Studies of the Mechanism of Anesthetic Action in Neurons; Dr. Charles Glabe, Fluorescent Probe Studies of the Interaction of the Sperm Egg Adhesion Protein Binding with Membranes.